What will you do when the power goes out? Even if you have solar panels on your roof, your answer will probably be “light a candle and wait it out.” Unless you know how to make it work.

It’s true: most solar panel systems aren’t designed to work during a power outage. Below, we’ll detail some options for people who want to use those solar kilowatt-hours even when grid goes down. But first, here’s a little background:

They say “the grid is your battery”

Most people with solar on their house have what’s called a “grid-tied” solar system, which means the panels are connected to an inverter and the inverter runs both to the main AC panel in the house and to a special smart electric meter that records both energy you use from the utility company and energy sent to the grid by your solar panels.

That’s why home solar people generally say “the grid is your battery.” When your solar panels are producing extra energy, you’re sending it out to your neighbors and getting credit for it, but when the sun goes down, you still need electricity from the utility company. If you play this balancing act just right, you can have a power bill near $0.

…until the power goes out

In the event of a blackout, a typical grid-tied system has a special automatic shut-off, to prevent that extra energy from being sent over power lines that may be damaged. It’s a safety feature intended to protect the line workers who go out to fix things when they break.

But that means your house doesn’t get the solar power either. In a blackout situation, the power from your solar panels goes… nowhere.

The best ways to back-up a grid-tied solar system

Maybe you’re thinking about installing solar, but you want to make sure you’ll have power if the grid goes down. Maybe you already installed solar and you’re looking for a simple way to upgrade your system to a hybrid with battery backup.

If you want to keep your house running when the power goes out, there are a few ways to do it:

Use a backup generator

Replace your inverter with a Sunny Boy

Go full hybrid with backup batteries

1. Using a backup generator

You solar lovers out there aren’t going to like this, but… the cheapest way to make sure you’ve got backup power in the event of a blackout is to buy a generator.

For around a thousand bucks—plus the costs of fuel and installing an external electrical plug—you can get a 7,000-plus-watt diesel generator that can run your whole house while the utility workers bring the grid back online (note: we’re not in the business of giving electrical systems advice. Consult a professional to setup this kind of system).

With your generator and some fuel, you can usually outlast any prolonged outage of the grid, and even help a neighbor out if you need to. Your solar panels will remain off until the grid comes back up, but at least you’ll have power.

But the name of this website isn’t “Diesel Power Rocks,” right? So let’s look at some purely solar options!

2. Replacing your inverter with a Sunny Boy

There’s one inverter on the market that is designed to allow you to use your solar power if the grid goes down, but the sun is still up. It’s called the Sunny Boy and it comes from a German company called SMA. It doesn’t give you full power, but if you need to keep some lights on and some devices charging, it’s the best way to do it.

While most solar inverters have that automatic shut-off we discussed above, the Sunny Boy has a special circuit that allows homeowners to switch over to pure solar power after a power outage.

A look at the Sunny Boy solution

Here’s how it works:

The home loses grid power

The homeowner (that’s you!) goes down to the Sunny Boy and flips a special switch on a junction box wired to the inverter.

The inverter directs power from the panels to an outlet in the junction box

You plug in necessary appliances to the outlet and live like a king while others suffer!

To be certain, this isn’t the solution if you want to run all your home appliances on just your solar panels. The Sunny Boy can only produce up to 2,000 watts of power at a time, and it’s designed to shut down if the power draw is too great. And again, it only works if the sun is up.

2,000 watts might sound like a lot (20 100-watt light bulbs!), but it probably isn’t enough to start an air conditioner. Realistically, you can probably plug in your fridge and a lamp, along with a radio and your smartphone to keep you company.

The total cost for the Sunny Boy and the outlet might be $2,500 more than another brand of inverter without the backup feature. But factored over a 10-year span (the life of the inverter), you might find this an attractive option.

If you want to keep your full house running even when the grid is down, the only way is with a hybrid grid-tied battery back-up system:

3. Using solar plus battery backup to keep your house running during a blackout

The true way to have your solar cake and eat it too is to go hybrid. With a grid-tied solar system backed up by a robust battery bank, you’ll have the certainty that the grid provides; no matter how much energy you need or when you need it, it’ll be there. But you’ll also have the peace of mind that comes with battery backup; if the grid goes down, you can run your appliances for as many days as you can afford batteries for.

And unless you’re fairly wealthy, what you can afford will definitely be the limiting factor here. A typical grid-tied solar system with 5 kilowatts of solar panels costs $15,000 (professionally installed, before the federal tax credit and other incentives), and adding a hybrid inverter and batteries to power a home for 2 days can easily add $15,000 – $20,000 to the price. And that’s just with big ol’ lead-acid deep cycle batteries.

How does a hybrid home solar system work?

A hybrid solar system is remarkably similar to an off-grid solar system. You’re still planning to be off the grid for up to a few days at a time and you’re still planning to mainly use solar power to make it happen. You’ll need some special equipment to keep the batteries charged at all times, and some additional wiring to make the system work during a blackout.

Here’s a great diagram of the system and how power travels from the panels to your home:

In the diagram above, solar energy follows the path pointed out by the arrows. The major components are the panels themselves, the charge controller that keeps the batteries charged and ready, the inverter that turns the DC solar power into AC power for your home, and the backup panel, which is always connected to your essential appliances.

That backup panel is important. If the power goes out, you probably won’t be needing the the pool pump or the home theater, but you probably do want your fridge, lights, and some other essential appliances. In the event of a power outage, all you have to do is turn off the AC disconnect (12 in the image above), and your batteries will provide as much power as you need to exactly the things you need most.

The bottom line for a solar system with battery backup

When the grid’s down, a hybrid system springs into action, essentially becoming an off-grid system. There’s a TON of information to learn about designing a system that can power your home with no grid power. Thankfully, we’ve developed an extensive off-grid solar page to help you learn!

If you’re interested in a hybrid grid-tied system, definitely check out what goes into choosing the panels, batteries, and other equipment for an off-grid solar system.

It would be very sad to have a $20,000 solar system installed and to be in the dark during a blackout. Would it be possible to connect an automatic disconnect or a DPDT contactor that would disconnect the grid in the event of a blackout, then with a small inverter powered by the sun we can excite the big inverter this way we can have solar power off the grid in case of a black out.

I think his point is the one you linked to is a GAS generator. I get you are solar guys, but there is a huge price difference between Gas generators and diesel generators, due to both basic engineering costs of the engine, and to economies of scale, since gas generators are sold in huge volumes, and diesel ones are pretty specialized.

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